Micromechanical structures, and in particular microelectromechanical systems, are employed in numerous technical fields and notably in the fabrication of sensors. These sensors are sometimes used in hostile environments, that is to say environments that have high temperatures or pressures, or extreme chemical conditions. For such applications, it is known to resort to microelectromechanical systems made of a resistant material such as silicon carbide (SiC). Indeed, this material has numerous advantages, notably its high mechanical strength and its inertia vis-à-vis most chemical agents.
Such sensors are known from the literature and described by N. Marsi et al. (The Mechanical and Electrical Effects of MEMS Capacitive Pressure Sensor Based 3C—SiC for Extreme Temperature, Journal of Engineering, Vol. 2014, Article ID 715167); D. J. Young et al. (High-Temperature Single-Crystal 3C—SiC Capacitive Pressure Sensor, IEEE Sensors Journal, Vol. 4, No 4, August 2004); G-S Chung (Fabrication and Characterization of a Polycrystalline 3C—SiC Piezoresistive Micro-pressure Sensor, Journal of the Korean Physical Society, Vol. 56, No 6, June 2010, pp 1759-1762); or instead by B. V. Cunning et al. (Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers, Nanotechnology, Vol. 25(32) p. 325301, 2014).
However, this chemical inertia has the consequence of making the production of micromechanical structures made of silicon carbide very difficult, because the agents normally used in conventional processes for fabricating microsystems are difficult to apply to silicon carbide. The document EP2168910B1 proposes a process in which a sacrificial silicon germanium (SiGe) structure is deposited and structured on a silicon carbide surface. This sacrificial structure is next covered by a silicon carbide layer. An opening is next arranged on the surface of the silicon carbide layer, this opening emerging on the sacrificial silicon germanium structure. A wet etching is next carried out, the etching agent penetrating via the opening arranged in the silicon carbide layer and attacking the sacrificial structure. Once the silicon germanium structure has been entirely etched, the opening arranged in the silicon carbide layer is closed again in order to obtain a cavity.
This process is not however without drawbacks. Firstly, in order to free the membrane, it is necessary to expose the sacrificial structure to the chemical etching agent, which imposes arranging an opening in the silicon carbide layer that next has to be closed again. In addition, the etching step necessitates a liquid chemical agent which may lead to a sticking effect of the silicon carbide structure induced by the surface tension of the etching agent or the rinsing agent making the micromechanical structure inoperable.
There thus exists a need for a process for fabricating a micromechanical structure made of silicon carbide comprising a cavity, for example a microelectromechanical system, not requiring arranging an opening in the silicon carbide layer to carry out the etching step and making it possible to prevent the phenomenon of adhesion of the membrane of the cavity during this etching step.